It depends if you have Windows or Linux OS. If you are using a 64-bit operating system, you will have to enable the 386 architecture because the server software is written in 32 bit which means each server can MAX use 4096MB of memory on both OS. To be sure i would recommend at least 16GB of RAM. And for SSD Storage the CSGO server takes about 25 GB of storage, if you are low on storage you can use symbolic links.
For optimal performance regarding CPU i would use Windows OS because server software has multi threading support, on linux its based on single thread performance. With that huge amount of players i would personally take a very close look at: https://browser.geekbench.com/processor-benchmarks
Hope this helps